Method of making rolling element bearings

ABSTRACT

Making rolling elements by forming low mass cores having either hollow centers or being of a low mass material. The low mass cores are plated and heat treated to provide hard surfaces on the rolling elements. After grinding to the proper diameter the rolling elements are assembled between races to form a bearing.

0 United States Patent 11 1 1111 3,781,958 Parker Jan. 1, 1974 METHOD OF MAKING ROLLING [56] References Cited ELEMENT E IN UNITED STATES PATENTS [75] inventor: Richard J. Parker, North Olmsted, 1,039,674 9/1912 Schatz 29/l48.4 B Ohio 2,177,928 10/1939 Knudsen 29/1484 B 2,978,794 4/1961 Lamson et al 29/1484 L Assigncer The United States of America 85 3,677,807 7/1972 Curtis et al 29/148.4 B represented by the Administrator of 3,685,113 8/1972 Hagenbach 29/148.4 B the National Aeronautics and Space Administration, Washington, DC. Primary ExaminerThomas H. Eager Filed g 14 1972 Attorney-N. T. Musial et a1.

[21] Appl. No.: 280,390 [57] ABSTRACT Related Application Data Making rolling elements by forming low mass cores [62] Division of Ser No 201 904 NOV 24 I97] having either hollow centers or being of a low mass material. The low mass cores are plated and heat treated to provide hard surfaces on the rolling elei ments. After grinding to the proper diameter the roll- [58] Fieid 29/148 4 148 4 B ing elements are assembled between races to form a 29/149.5 NM, 148.4 R, 149.5 PM

bearing.

8 Claims, 3 Drawing Figures METHOD OF MAKING ROLLING ELEMENT BEARINGS RELATED APPLICATION This application is a division of copending application Ser. No. 201,904 which was filed Nov. 24, 1971.

ORIGIN OF THE INVENTION The invention described herein was made by an employee of the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefor.

PRIOR ART This invention is concerned with a method of making an improved bearing having low mass rolling elements. The invention is particularly directed to making rolling elements having lightweight cores that are plated.

When conventional rolling-element bearings are used at high rotative speeds centrifugal forces of the rolling elements on the outer races are detrimental to bearing life. Low mass rolling elements reduce this centrifugal force thereby increasing the life and reliability of high speed bearings.

Low mass rolling elements, such as hollow balls and rollers, are used in bearings on shafts which start and stop quickly. Less energy is required for acceleration and deceleration with hollow rolling elements because of their low inertia.

Low mass rolling elements can be fabricated of a material with a density significantly less than bearing steels. Other low mass rolling elements are hollow to reduce the mass. In either hollow rolling elements or those of low density material the fatigue strengtlrmust not be less than that of solid elements of high quality bearing steel. Rolling elements of relatively low density material have shown much lower fatigue strength than have conventional balls and rollers. Hollow balls of conventional bearing steels with significant mass reduction have shown either a weakness in the weld material or flexure fatigue of the wall. 1

SUMMARY OF THE INVENTION These problems have been solved by making low mass rolling elements in accordance with the present invention and using them in improved bearings. Low mass rolling elements are produced by forming hollow cores of an inexpensive steel. Also a lightweight material can be used to make a low mass solid core. The low mass solid core and the hollow core are plated with iron and heat treated to form a hard surface.

OBJECTS OF THE INVENTION It is, therefore, an object of the present invention to provide a method of making low mass rolling elements having a high fatigue strength and high resistance to flexure fatigue for use in bearings.

Another object of the invention is to provide a method of making low mass rolling elements whose fatigue strength is as good as or better than solid rolling elements of conventional materials.

A- further object of the invention is to produce low mass balls to increase the life and reliability of high speed ball bearings.

These and other objects of the invention will be apparent from the specification which follows and from the drawing wherein like numerals are used throughout to identify like parts.

DESCRIPTION OF THE DRAWING FIG. 1 is a vertical section view through a rolling element bearing having a rolling element constructed in accordance with the invention;

FIG. 2 is an enlarged sectional view taken along the line 22 in FIG. 1; and

FIG. 3 is an enlarged vertical section view similar to FIG. 2 showing an alternate embodiment of the inventlon.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing there is shown in FIG. 1 an improved rolling element bearing assembly 10 of the ball bearing type. The bearing assembly 10 comprises an outer race 12 spaced from the inner race 14. Rolling elements 16 in the form of balls roll between the outer race 12 and the inner race 14. The balls are properly spaced by a separator 18 or cage.

According to the present invention the rolling element 16 is made up of either a hollow core 20 shown in FIG. 2 or a solid lightweight core 22 shown in FIG. 3. Both the cores 20 and 22 are covered by a plated surface material 24.

The hollow core 20 shown in FIG. 2 is made by forming a hollow sphere of inexpensive low carbon or medium carbon steel. This hollow sphere 20 is fabricated by welding together two hemispheres of the low carbon or medium carbon steel. This can be accomplished in accordance with the teachings of copending application Ser. No. 196,917 by Thomas Moore entitled Production of Hollow Components for Rolling Element Bearings by Diffusion Welding which was filed Nov. 9, I971.

The lightweight solid core 22 shown in FIG. 3 is made of relatively low density material, such as aluminum oxide. This core 22 is formed by cold pressing and sintering, hot pressing, or other powder metallurgy techniques.

The hollow spherical core 20 and the lightweight core 22 are plated with pure iron. This is accomplished by electrolytic deposition, ion plating, or sputtering.

The plated cores are then heat treated by a case hardening process. Carburizing has been satisfactory. The plated cores are then ground and finished to the required tolerances.

Each rolling element 16 has a low mass and a hard homogeneous surface with a relatively soft and ductile inner core. The hardness of the iron plating 24 is between Rockwell C 60 and 65. The thickness of the finished iron plated surface is preferably at least twice the depth of the maximum shear stress expected in the application. This thickness is on the order of 0.012. to 0.015 inch. The homogeneous iron 24 is inclusion free and can provide rolling-element fatigue strength equal to or better than conventional high quality bearing steels. The relatively soft ductile inner hollow core 20 eliminates the problem of flexure fatigue of the wall. N0 flexure problem is encountered in the solid core 22.

The races 12 and 14 are fabricated from ring shaped blanks of a high hardenability bearing steel, such as AISI M-50. The blanks are heat treated to a Rockwell C hardness of 58 or greater. The ring blanks are than ground to specified dimensions to form an inner race and an outer race.

Although a preferred embodiment of the invention has been described it will be appreciated that various modifications may be made without departing from the spirit of the invention or the scope of the subjoined claims. The bearing assembly can be made to form an angular contact ball bearing to accommodate radial or thrust loads or to form deep groove ball bearings to take primarily radial loads.

What is claimed is:

l. A method of making a rolling element bearing comprising the steps of forming a pair of races,

forming a plurality of cores having a low mass,

plating the surfaces of said cores to form a coating,

heat treating said plated cores to harden said coating, grinding the plated cores to a predetermined diameter, and

assembling said plated cores between said races.

2. A method as claimed in claim 1 including the step of joining preformed components to form a hollow core.

3. A method as claimed in claim 2 wherein the components are steel.

4. A method as claimed in claim 1 wherein the coating is iron.

5. A method as claimed in claim 1 including the step of forming a solid core of a low density material.

6. A method as claimed in claim 5 wherein the solid core has a density less than the density of the coating.

7. A method as claimed in claim 5 wherein the low density material is aluminum oxide.

8. A method as claimed in claim 1 wherein the plated cores are carburized to harden same.

l =l l 

1. A method of making a rolling element bearing comprising the steps of forming a pair of races, forming a plurality of cores having a low mass, plating the surfaces of said cores to form a coating, heat treating said plated cores to harden said coating, grinding the plated cores to a predetermined diameter, and assembling said plated cores between said races.
 2. A method as claimed in claim 1 including the step of joining preformed components to form a hollow core.
 3. A method as claimed in claim 2 wherein the components are steel.
 4. A method as claimed in claim 1 wherein the coating is iron.
 5. A method as claimed in claim 1 including the step of forming a solid core of a low density material.
 6. A method as claimed in claim 5 wherein the solid core has a density less than the density of the coating.
 7. A method as claimed in claim 5 wherein the low density material is aluminum oxide.
 8. A method as claimed in claim 1 wherein the plated cores are carburized to harden same. 